Root crop harvesters must be designed to carry the root crop from the ground to a collection station. During that process, debris such as dirt, small stones and vines must be removed without causing damage to the root crop itself.
Typical harvesters for root crops comprise driven endless rod chain conveyors which are either belted chains or hook chains. Root crops such as potatoes are carried on top of generally parallel rod members of the conveyor and smaller materials such as dirt and rocks are able to fall downwardly between the individual rod members.
In order to better remove dirt, rocks and clinging vines from the root crops, harvesters typically include some form of shaker assembly which attempts to set up a steady shaking motion to the chain conveyors. The shaker assemblies are secured to the frame of the conveyor and typically include a multi-lobed member which, as it rotates, allows the conveyor to fall and then suddenly throws the conveyor rods upwardly when a lobe reaches its peak height. An example of such a shaker assembly is seen in U.S. Pat. No. 3,106,249 to Zachery. Zachery describes a harvester for potatoes which has a shaker assembly consisting of a three lobed member. Such traditional shaker assemblies are undesirable in that too severe a shaking is imparted to the conveyor. As such shaker assemblies turn they pick the chain up and move substantially in a lateral direction before reaching the apex. The shakers, only contact every third or fourth rod. This low frequency motion acts like a launching pad. Potatoes, for example, are thrown up into the air and upon landing back on the conveyor are bruised. Bruising causes farmers to lose a great deal of the value of their harvest.
Alternative shaker assemblies have been devised in which numerous lobes are created such that the conveyor is alternatively lifted and lowered more often which results in less violent action on the part of the root crop on the surface of the conveyor. In some schemes, the shaker assemblies are adjustable up and down with hydraulic controls such that the operator can adjust the amount of tossing of the root crop on the conveyor. Such systems, however, require effort in setting up properly.
Other alternatives have been to use large driven rollers which are quite large relative to the spacing between the rods. Of course the drive mechanisms makes the driven rollers more expensive and entail another mechanism which may result in down time.
Another difficulty with prior art devices is that they tend to operate differently depending on the load of the material on the conveyor. Therefore, even in adjustable systems, a conveyor will not be properly adjusted for adequate, yet non-bruising shaking if the weight of dirt and potatoes on the conveyor changes markedly.